The present invention relates to polymer optical waveguides.
Optical waveguides can be formed in polymers by using a core polymer and a cladding polymer with the core polymer refractive index being slightly higher than that of the cladding polymer (typically 0.3-1%) in the near infrared region of the optical telecommunication wavelength window. In order to form useful optical waveguide devices such as integrated splitters, couplers, arrayed waveguide gratings, and optical waveguide amplifiers, it is essential to have low loss optical waveguides with minimal temperature dependencies. Temperature variations affect several waveguide properties, such as birefringence, refractive indices of the core and the cladding, waveguide loss, etc, largely through a coefficient of thermal expansion (CTE) mismatch between the waveguide layer and the substrate.
A general approach of making polymer optical waveguides is to put an undercladding polymer film layer on a substrate and then a polymer core film layer on top of the undercladding layer. The polymer core layer film subsequently undergoes lithographic and etching processes from which a rectangular cross-section channel is formed. An overcladding polymer film layer is then put on top of the waveguide core and the undercladding. Polymers with CH bonds typically have high absorption in the infrared region where the optical communication signals reside. This high absorption causes optical communication signal loss. To reduce such loss, CF bonds are used to substitute the CH bonds in the waveguide core and cladding polymers. Perfluorinated polymers have no CH bonds, resulting in extremely low absorption loss around the 1.5 xcexcm and 1.3 cm infrared communication wavelengths.
It has been found that, during the processes of forming the undercladding, core and overcladding layers, such as spin coating and subsequent drying of the solvents, temperature changes usually occur around the polymer waveguide layers. Such temperature variation causes polymer shrinkage or expansion in accordance with the CTE of the polymer materials. In the meantime, the waveguide substrate undergoes similar processes as temperature changes. As a silicon wafer is the usual substrate platform for polymer waveguides, the mismatch of CTE between the silicon wafer (CTE of approximately 4 ppm per degree Celsius) and the polymer waveguide cladding and core (CTE of typically between 50 and 100 ppm per degree Celsius) can cause stress build-up and polymer film microcracking in the polymer layers. These effects will increase the polymer waveguide attenuation, increase the polarization dependence of the waveguide, and require the waveguide devices to be temperature stabilized.
It has been demonstrated in U.S. patent application Ser. No. 10/045,317, filed on Nov. 7, 2001, which is owned by the assignee of the present invention and which is incorporated herein by reference in its entirety, that by using polymer substrates for polymer waveguides, the CTE mismatch induced problems can be greatly alleviated. It is desirable to further eliminate the CTE mismatch induced problems to minimal level by eliminating the substrate.
Briefly, the present invention provides an optical waveguide. The waveguide is comprised of a first cladding layer having a first exposed surface portion and a second surface portion generally opposing the first exposed surface portion, and a core disposed on a portion of the second surface portion. The core has a first end and a second end. The waveguide is also comprised of a second cladding layer having a first exposed surface portion and a second surface portion generally opposing the first exposed surface portion. The second surface portion of the second cladding layer is disposed on the core and a remaining portion of the second surface portion of the first cladding layer.
Additionally, the present invention provides a method of manufacturing a waveguide. The method comprises providing a substrate; disposing a first material onto the substrate; disposing at least a second material onto the first material; and engaging at least the first material with a solvent, the solvent dissolving the first material and separating the at least second material from the substrate.
Further, the present invention also provides an optical waveguide assembly. The assembly is comprised of an optical waveguide including a first cladding layer having a first exposed surface portion and a second surface portion generally opposing the first exposed surface portion, and a core disposed on a portion of the second surface portion. The core has a first end and a second end. The waveguide also includes a second cladding layer having a first exposed surface portion and a second surface portion generally opposing the first exposed surface portion. The second surface portion of the second cladding layer is disposed on the core and a remaining portion of the second surface portion of the first cladding layer. The assembly is also comprised of a first support structure disposed on at least one of the first cladding layer and the second cladding layer, proximate the first end of the core and a second support structure disposed on at least one of the first cladding layer and the second cladding layer, proximate the second end of the core. The assembly is further comprised of a support surface engaging each of the first and second support structures.